Polyarylene sulfide (also called “PAS” hereinafter), represented by polyphenylene sulfide (also called “PPS” hereinafter), is an engineering plastic having excellent heat resistance, chemical resistance, flame retardancy, mechanical strength, electrical characteristics, dimensional stability, and the like. PAS has been widely used in a wide variety of fields, such as electric/electronic devices and devices for automobiles, since PAS can be formed into various molded products, films, sheets, fibers, and the like by ordinary melt processing methods, such as extrusion molding, injection molding, and compression molding.
A known representative production method for PAS is a method of obtaining PAS such as PPS by performing a polymerization reaction on a sulfur source and a dihalo aromatic compound such as p-dichlorobenzene (also called “PDCB” hereafter) while heating (for example, temperature conditions of approximately 175 to 350° C.) using a mixture containing a polar organic solvent such as N-methyl-2-pyrrolidone (also called “NMP” hereafter) (Patent Documents 1 and 2). Other known methods for producing PAS with a high molecular weight include a two-stage polymerization method of performing a polymerization reaction while changing the polymerization temperature and the water content present in the polymerization reaction system, and a method of performing polymerization using a phase separation agent as necessary (Patent Documents 3 and 4).
A roughly cylindrical reaction vessel (also called a “polymerization vessel” or a “polymerization can”) equipped with a stirring device is often used as a PAS polymerization device. It is necessary to precisely control the compositions of the polar organic solvent, the raw material monomers, and the generated PAS polymer inside the polymerization device, specifically, inside the reaction vessel. Therefore, PAS polymerization is performed by using a reaction vessel provided with a mixing impeller, supplying raw material monomers, a solvent (polar organic solvent, water, or the like), a polymerization aid, and the like from one or a plurality of supply tubes provided at the top part of the reaction vessel, adjusting the inside of the reaction vessel to a prescribed temperature and pressure and changing the temperature and pressure as necessary, additionally supplying raw material monomers, a solvent, or the like, and performing a polymerization reaction while sufficiently stirring. The produced PAS polymer is extracted from a discharge tube ordinarily provided at the base of the reaction vessel, and a PAS polymer product is obtained via washing, purification, or the like.
At the time of stirring in the roughly cylindrical vessel, it is known that a co-rotation phenomenon occurs, wherein a liquid current rotates in the form of a vortex along the vessel wall as the mixing impeller rotates. When the co-rotation phenomenon occurs, the rotation flow in the circumferential direction becomes dominant, and the liquid current in the vertical direction becomes difficult to generate, which makes it difficult to homogenize the composition of the stirred matter inside the vessel or to uniformly mix the stirred content. In this case, a forced vortex (forced vortex zone) which co-rotates together with the mixing impeller and a free vortex on the outside thereof are formed, so a pressure difference arises between the central part of the vessel and the vessel walls, which causes a cavity to be formed in the central part of the liquid surface. Therefore, a baffle (baffle board) is often inserted to convert the rotation flow in the circumferential direction to a vertical circulation by obstructing flow in the circumferential direction. The insertion of a baffle (baffle board) generates a vertical circulation together with the rotation flow in the circumferential direction. As a result, it is possible to realize the enhancement of stirring efficiency (increase in the stirring power number, enhancement of shear performance, or the like), the formation of a prescribed flow pattern, and the securing of heating surface area, which makes it possible to achieve the homogenization of the composition of the stirred matter or the uniform mixing of the stirred matter, the homogenization of a prescribed reaction, or the like.
In many cases, a member in the shape of a flat plate, a rod, or the like extending in the vertical direction of the vessel parallel to the vessel walls in close proximity to the vessel walls is used as a baffle (baffle board). It is known that the mixing effect or the like differs as a result of changing conditions such as the shape or size (width, diameter, length, or the like) of the baffle, the length below the liquid surface (also called the “interface”), and the gap relative to the vessel wall. In addition, a passage for a coolant or a heating medium may also be provided inside a baffle (baffle board) so that the baffle may be used as a temperature adjustment device. The following are known methods of attaching a baffle (baffle board): (1) fixing a baffle to the body portion of the vessel by welding or the like; (2) fixing a baffle with an attachment fitting provided in the vessel (also called a “baffle support” or a “baffle support part”); and (3) suspending and fixing a baffle with a nozzle or the like provided on the lid of the vessel (Patent Documents 5 and 6). Patent Document 5, for example, discloses: that in the case of (1), welding or cutting of the welded part is necessary in order to attach or replace the baffle board, so the number of operation man-hours is high, and the operation time also becomes long; that in the case of (2), the replacement or the like of the baffle board is easy, but attachment fittings must be additionally provided by welding or the like in order to increase the number of baffle boards installed, which leads to problems in that the number of operation man-hours becomes high; and that in the case of (3), it is not possible to provide a greater number of baffle boards than the number of nozzles, and since the force applied to the baffle boards is supported by the lid, there are problems in that the usage conditions are restricted.
In a PAS production device, deposits may accumulate in step with the stirring operation or the like inside the reaction vessel. The composition of deposits primarily consists of a PAS polymer as a product and NaCl as a by-product, but low polymers of PAS (including oligomers or the like) or unreacted raw material monomers or alkaline substances (NaOH or the like) may also be contained. As the accumulation of deposits on the baffle, the baffle support, the supply tubes, or the like progresses, the accumulated deposits may peel and drop off, and the deposits may be mixed in the resulting PAS product, which may lead to a reduction in quality or may inhibit the discharge of PAS from the reaction vessel. Further, when the deposits come into contact with high concentrations of alkaline substances at high temperatures, there is also a risk that the corrosion of the device (supply tubes, vessel walls, or the like) may occur. The accumulation of deposits becomes more prominent as the number of polymerization batches is increased. Thus, it is necessary to periodically stop the polymerization reaction completely and devote an excessive amount of labor and time to cleaning the reaction vessel (removal of deposits or the like).
Therefore, there is a demand to provide a PAS production device which suppresses the accumulation of deposits on a baffle (baffle board) or the like disposed inside a reaction vessel via a baffle support for the purpose of enhanced stirring efficiency or the like, thereby contributing to enhanced production efficiency, reduced cost of removing accumulation, and enhanced quality of the PAS product.